1. Field of the Invention
The present invention relates generally to hydraulic dampers for vehicles and, in particular, is concerned with a piston and piston rod subassembly and a method of manufacture and assembly.
2. Description of the Related Art
A typical hydraulic shock absorber or strut includes a piston and piston rod subassembly which reciprocates in an inner cylinder during compression and rebound of the damper. The piston may contain a valving package to vary the flow of hydraulic fluid from first and second chambers in the inner cylinder, resulting in desired damping characteristics.
The piston is generally formed as a solid cylindrical member requiring several machining and cutting operations. An inner passage is bored through the piston to receive the valving package and permit the flow of fluid. Oftentimes, the valving package is retained within the piston by a crimping procedure. A sealing band can be provided around the outer circumference of the piston to provide a seal against the inner surface of the inner cylinder. In other constructions, a piston can be formed by various elements into a substantially cylindrical package capable of reciprocating in the inner cylinder.
In the majority of shock absorbers and struts, the piston is either mounted on a threaded piston rod or welded to the piston rod. Drawbacks can occur with either one of these mounting techniques. Threading a piston rod increases manufacturing and assembly costs. Furthermore, the joint between the piston and the rod can become loose during operation. An example of a threaded piston rod can be found in U.S. Pat. No. 3,901,359.
While welding a piston to the rod may be less expensive than threading the rod, the heat generated by the welding process can distort the piston and its concentricity. Lack of concentricity can cause a piston to bind as the rod reciprocates in a damper, resulting in a defective unit. Second, weld spatter can become attached on and may adversely affect the valving, thereby interfering with fluid flow. Also, heat from the welding operation to attach the piston to the rod may damage the sealing band provided on the outer circumference of the piston. An example of a welded piston can be found in U.S. Pat. No. 3,724,615.
While conventional piston and piston rod subassemblies are successfully utilized, the art continues to seek improvements. It is desirable to provide a piston housing for containing a valving package which can be economically mounted on the piston rod without damaging the piston. Specifically, it is desirable to provide a piston and piston rod subassembly without the expense of current threading operations and/or the potentially adverse effects of welding.